JPS58224107A - Refining method of molten iron - Google Patents

Abstract

PURPOSE:To generate and recover a large amt. of CO-contg. gas while obtaining an optimum cooling effect with limestone by adding the limestone into a refining furnace for molten iron at the speed of addition or the amt. of addition per time controlled within a prescribed range, at a suitable timing in the process of refining. CONSTITUTION:Limestone (CaCO3) is added into a refining furnace for molten iron at <=0.083kg/T-steel.sec addition speed or at <=2.5kg/T-steel.time each time at the time when the [Si] in the molten iron is <=0.01wt% and [C] is allowed to remain at >=0.8%, in the process for refining of the molten iron. The limestone to be added is used preferably in the form of grains of 5-50mm. diameter. The limestone can be added continuously or intermittently by a method of sealing the same in a metallic case, paper bag, cloth bag or the like or feeding the same with a rotary feeder. It is preferable to progress reaction smoothly and thoroughly to add the limestone near the fire point in the part in the refining furnace where oxygen is blown to the molten iron.

Description

[Detailed Description of the Invention] This invention relates to a molten iron smelting furnace method, in particular, in a converter, limestone (CaCOs) is efficiently added to the steel bath from above in the most rational way, and limestone (CaCOs) is produced by thermal decomposition. This invention relates to a novel refining method in which CO□ gas is reacted with (C) in a steel bath to promote stirring of the steel bath and to generate a large amount of gas with a high co gas ratio.

Exhaust gas recovery devices are currently installed in many converters, and the exhaust gas generated from the converter during blowing is recovered without combustion (hereinafter referred to as the OG method). This recovered converter exhaust gas contains a large amount of CO, so it has become a valuable energy source considering the recent rise in oil prices. Conventionally, the following methods have been used to improve the amount of energy in the recovered exhaust gas.

■ Improving the OG gas recovery charge ratio, ■ Reducing air entrainment in order to recover CO generated from the converter without burning it as much as possible, ■ Time from the start of blowing to the start of the OG method, and To shorten the time from the end of the OG method to the end of blowing as much as possible,
That is, the exhaust gas recovery time during blowing is lengthened. For example, it can shorten the time required to analyze exhaust gas components.

However, the amount of CO gas generated from the converter is limited.
Furthermore, there are limits to the above method due to safety considerations, such as the need to prevent the exhaust gas from becoming explosive.

Therefore, the idea that the converter-exhaust gas recovery device is not limited to the mere function of collecting generated gas, but is more actively used as an energy integrated system conversion and recovery device has been born. As one of the methods, a method has been attempted in which coke, coal, or the like is charged into a converter as a Ca source, and the materials are reacted in the furnace to be converted into CO gas and recovered. However, this method [Ca to CO
In order to achieve this, many oxygen sources must be added, and considering the costs of coke and coal, no significant benefits can be expected.

Recently, Japanese Patent Application Laid-Open No. 123318/1983 has proposed a method for increasing the recovery of Co gas by injecting pulverized limestone together with a carrier gas through a tuyere provided at the bottom of the furnace. This means that even if limestone is put into the converter from above, it will decompose through the reaction CaCO3→CaO+ CO2, and C
This was proposed because it was not possible to improve the amount of exhaust gas recovered by only producing aO and CO2 gas. Although the proponent's ingenuity is lacking in this point, this method requires the limestone to be crushed into fine particles in order to be transported by gas, and also requires a huge investment in blowing equipment, etc. This method cannot necessarily be an industrial method that is useful for industrial development because it has fundamental problems such as extremely increased maintenance such as safety management against wear of piping.

Therefore, the inventor of the present invention has added limestone into the furnace from above the steel bath using conventional equipment and methods without using any special equipment, which is a rational and efficient way to satisfy the original cooling effect of limestone. , and conducted experiments and studies on a method to efficiently generate a large amount of CO gas, and found that the desired method could be implemented by operating within a specified range of limestone addition timing, addition rate, and amount of addition per time. .

CaCO5+CaO+CO2(i) Co2+C→2CO(2) (However, equation (1) is P Co 2 = 1 at around 900°C
'Lm.

Furthermore, equation (2) actively progresses at temperatures above 1000°C.)
The present invention was made based on this new knowledge, and its characteristics are that in the molten iron refining process, the [S1] of the molten iron is 0.01 weight or less, and the (C) is 0.8
When limestone remains in the molten iron smelting furnace at a maximum speed of 0.083 kll/T-steel-s
Less than ec or up to 2.5 kl! / T-stsel・
The purpose is to efficiently generate and recover a large amount of CO-containing gas while obtaining an optimal cooling effect by adding it in batches.

In other words, the present invention is applicable to the so-called silicon blowing process in the early stage of blowing in a converter (when [separate] in the bath combines with 02
5102] ends, that is, the time when (Sl) in the bath becomes 0.01 wt- or less, until the time when the wt% of (C) in the bath becomes less than 0.8 0.083kg/+5teel・8 at any time between
with addition rate below ee or 2.5 kg/T-5
By adding limestone in portions of 1/2 times or less, it is possible to efficiently generate and recover a large amount of CO gas.

The details of the configuration of the present invention will be explained below.

First, when limestone is added to the converter, the above (1) and (2)
Whether or not these reactions are being carried out sufficiently can be determined from the heat balance in the converter by how close the cooling capacity for C and aCo 5 is to the theoretical value. Therefore, assuming that equations (1) and (2) each proceed at an efficiency of 100 cm, the substances produced from CaCO3 are CaO and CO, and the cooling capacity of this produced 90 aO is so-called 8 c '
= 0.60, and since the CaO content in limestone is approximately 56 cm, its cooling capacity is 110.34. Also Q, ((
1) The heat of reaction in equation 1) is the same (8c' = 1.1 in terms of Sc')
It is 0. Similarly, Q2 (heat of reaction in equation (2)) is Sc'=
It becomes 0.95. Sensible heat loss due to increased gas generation is S
It is calculated as c←0.29.

Therefore, the cooling capacity that CaCO3 has is 8c'=2
．． It becomes 68.

The above can be summarized as shown in Table 1.

Table 1 Using the cooling effect of Cm Co 3 as an index, the optimum conditions for the present invention were found.

■ Regarding the timing of addition of limestone in the present invention: Figure 1 shows that in a converter of 340 T/Heat, LDG (converter exhaust gas m
2000 kcat/Nm3 conversion. The following shows how the amount collected has changed. The conditions from the addition time to [F] in the figure are as shown in Table 2.

From Fig. 1, immediately after the section (■), that is, the [S1] in the molten iron became 0.01% by weight or less (St), after the blowing ended,
The maximum amount of LDG can be recovered when the molten iron is introduced at a time when (C) = O, S*.

At this time, the endothermic reaction according to equation (2) above occurs at an efficiency of approximately 100 cm, as shown in FIG.

This is supported by the fact that the apparent cooling capacity (Sc) of limestone is 2.66 in the section (■), which is almost the theoretical value6 (No. On the other hand, when [Sl] is present in excess of 0.01% by weight ■■, or when [C] is less than 0.8% by weight ◎ Even if limestone is added to [F] The amount of LDG recovered decreases because the reaction of equation (2) does not take place sufficiently due to the preferential oxidation reaction between dissolved 02 and [S1] in the molten iron and the rate-limiting [C] diffusion due to the low [C] concentration. Resulting in.

From the above, the timing of adding limestone in the present invention is (s
s) is 0.01% by weight or less, and (C') is 0.8
This is defined as the period when the content is present at % by weight or more.

■About the means of adding limestone: The following four methods are typical as means of adding limestone.
It is not limited to this.

■ Continuous addition using a rotary or 8-belt or vibrating feeder; ■ Intermittent addition using force or tongs; ■ Continuous or continuous addition of limestone in the form of a metal container and/or cloth or paper bag. /or a method of adding intermittently in parts; ■a method of filling a cylindrical body with limestone and adding continuously;■About the amount added per time when adding limestone intermittently: Figure 4 shows the amount of limestone added per heat. Same amount of limestone per unit (12 to 9/T)
atael) when added in several parts
It shows the amount of DG recovered.

As is clear from the figure, when limestone is added in portions by cut r-), the amount added per time is 2-5 kll.
/ T -5 teets, the amount of LOG recovered rapidly decreases (2).
The time lag before the reaction of the formula occurs is 69, and the time required for the reaction itself is short, so it is 2.5 kli/
If an amount exceeding T-steel is added at once, (1)
This is because the reaction of the formula and the subsequent reaction of the formula (2) occur explosively, and the efficient recovery of LDG is hindered by blowing out of the furnace mouth, sudden slopping, etc.

For the above reasons, the amount of intermittent addition in the present invention is 2.
The upper limit is 5 to 9/T-steel times.

■About the addition rate in the case of continuous addition of limestone: Figure 5 shows the results of investigating changes in the amount of LDG recovered by changing the continuous addition rate of limestone. As is clear from the figure, the addition rate was '0.083 kfl/T-steel-sec.
If the amount of gas is exceeded, the amount of gas generated instantaneously exceeds the generally established stable operation range of the IDF (large exhaust gas recovery fan), and suction is no longer possible. L.D.
G Katis to it-g O5, LDG (101ffi□
Ka5ゎ, □ decreases. (In order to cope with such an instantaneous increase in the amount of gas, unrealistic and huge equipment is required and it is not industrially possible.) In the same figure, a feeder was used as a continuous addition method.

For the above reasons, the continuous addition rate in the present invention is
The upper limit is 0.083 kg/T-steel-sec.

Next, FIGS. 6 to 9 show the effects on various operational indicators of molten iron refining when operating within the range of each optimum condition of the present invention described above. As is clear from these figures, the method of adding limestone in the present invention improves all of the slag [Mn], slag [p], slag T, Fe, and slag slag conversion rate of refined molten iron. ), and stable molten iron smelting operations are maintained.

This indicates that the reaction of formula (1) has proceeded almost completely and that the CaO content in the limestone is working effectively as quicklime content.

Next, add a preferable condition to these three conditions □
'The particle size range of limestone is mentioned.

Figure 10 shows the LD when the particle size of added limestone is changed.
It shows the change in G recovery. As is clear from the figure, for powdered limestone with a particle size of less than 5 mφ, the amount of LDG recovered decreases because it does not reach the molten iron in the furnace when it is added upward, except when using containers, bags, etc. shown by the dotted line. do. In addition, the particle size is 50m
In coarse-grained limestone that exceeds φ, unreacted limestone valves remain in the center of the grains, so the amount of LDG recovered also decreases.

Next, as for the place where limestone is added, especially in the case of a top-blown converter,
The oxygen blowing part on the bath surface in the furnace is preferably near the so-called fire point, and may be within a range of 1/2 the diameter of the furnace from the fire point. In other words, the goal is to melt the limestone quickly and create a slag-like state that works well for dephosphorization. This does not apply to bottom blowing converters.

Examples of the present invention are shown in Table 3 below. In addition, in this example, the upper blow of 340 T/Hat and the upper blow
Targeted are bottom-blowing converters.

As is clear from the above explanation, the present invention is applicable to the molten iron refining process, when the molten iron has [S1] of 0.01% by weight or less and [C] of 0.8% by weight or more remaining. Maximum speed of limestone in smelting furnace 0.083kIi/T-st
Continuously add eel/ssc or 2.5k
g/T-steel・Since it is added intermittently by dividing it into less than 100 g/T-steel, the intended purpose of molten iron refining can be stably maintained,
Moreover, it is possible to generate and recover a large amount of CO gas with high efficiency while sufficiently obtaining the cooling ability of limestone.

This eliminates the need to add coke, coal, etc. to the furnace as a [C] source and to supply an additional oxygen source for it as in the past, and it also eliminates the need to pulverize limestone and blow it from the slats installed at the bottom of the furnace. It is an industrially and economically advantageous method that can be made to function in the same way as the other methods without requiring any additional effort, and the industrial benefits are extremely large.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the time of addition of limestone and the amount of LDG recovered, Figure 2 shows the relationship between the time of addition of limestone and the reaction efficiency of equation (2) in the text, and Figure 3 shows the relationship between the time of addition of limestone and the amount of LDG recovered. Figure 4 shows the relationship between the time and the apparent cooling capacity of limestone (so-called 8c'), Figure 4 shows the relationship between the limestone addition method and the amount of LDG recovered, and Figure 5 shows the relationship between the limestone addition rate and the amount of LDG recovered. Figures 6 to 9 are diagrams showing the relationship between the amount of limestone added and the slag formation rate of T, Fe, [c], [p), and slag, and Figure 10 is the center of limestone. FIG. 3 is a diagram showing the relationship between particle size and LOG recovery amount. Patent applicant Nippon Steel Corporation 81st fan 2nd ■ ■ @ @ ■ ■ ■ @ O■ Rei 4th XyXXyRJo quantity (1 (1/7.5ted times) 1.
1. ! ;1. H31), 1I6a ρ673
1. θIll 6. /l)j 1. /177Erl
fJa *ACJu(kl/r5 teal je
c) Fan 2 Figure θJθ1oq, 0 /2.0 /, j:0
/11.0 limestone, t>fill (kl/T・5
leel)n 7 Figure stone 3Xy4AOt (kl/r-5〆eel) 88th

Claims (5)

[Claims] (1) In the process of refining molten iron, (St) of molten iron is 0.
Limestone (CaCO3
) with a maximum speed of 0.083kg/T-stesl・se
A method for refining molten iron, characterized in that it is added by c. (2) In the process of refining molten iron, (St) of molten iron is 0.
Limestone (caco3
) is added in a maximum of 2.5 kg/T-@tee times. (3) The method for refining molten iron according to claims 1 and 2, characterized in that limestone having grain diameters ranging from 5 m to 50 m+ is used. (4) A method for refining molten iron according to claims 1, 2, and 3, characterized in that limestone is added to the smelting furnace in the form of being sealed in a metal container, paper bag, cloth bag, etc. . (5) Claims 1 and 2, characterized in that limestone is added to the molten iron oxygen injection part in the smelting furnace.
The method for refining molten iron according to items 3 and 4.